Easy, my dumb level-0 car can tell me when it's icy. And finding lane markers is one of the easiest tasks in self driving (the hard part is knowing when to ignore them).
It's not a matter of "finding" lane markers. There are no lane markers visible after it snows.
We ourselves identify and confirm other urban waymarks via captcha which feeds the nav data -- bridges, signs, hills, hydrants, chimneys, lights. There is mass live verification from android auto in vehicles. There are many yearly layers of street view images and scans.
I don't think we'll see a system that can handle that in my lifetime.